Conventional "on-edge" mail stacking systems are usually composed of a transport followed by various forms of stacking mechanisms. Generally, multi-bin on-edge stacking systems include gating mechanisms which divert specific envelopes into predetermined stacker bins. Such on-edge stacking systems are well known. The overwhelming majority of these systems stack envelopes received in a vertical orientation on a horizontal surface commonly referred to as a stacker deck.
Typically, in an on-edge stacking system envelopes are transported vertically along a dual belt transport system, deflected into a stacker bin by a deflector mechanism, and guided into the bin by conventional guide and urging components. The conventional guides are generally flat surfaces that are made of low abrasive material so as not to interfere with the envelope being urged to the registration surface. The envelopes always stop against some sort of vertical registration surface. The integrity of the on-edge stacking is facilitated by a flat surface, commonly referred to as a paddle, that is orthogonal to the registration surface and is generally spring loaded or biased to maintain a tight stacking of the envelopes against the guide component.
The objective of mail stacking systems is to produce a tight bundle of envelopes where the bottom edge of the envelopes are resting on the horizontal surface and a lead edge of the envelopes are aligned against the vertical registration surface. This arrangement produces a stack of envelopes where the corners of each envelope formed by the bottom edge and the lead edge are perfectly aligned in two directions forming a neat stack of envelopes.
Although such systems have proved to be generally suitable for stacking most envelope types of envelopes, a problem has been recognized that the bottom edges of some types of envelopes do not properly come to rest on the horizontal surfaces. Most typically, this problem has been observed with respect to large envelopes. However, other types of envelopes are also susceptible to this problem. This problem is generally due to the normal force applied to the stack by the paddle which compresses the stack against the guides. The normal force must be large enough to produce a tight stack and yet small enough to allow an envelope fed into the stacker bin to reach the vertical surface and accordingly displace the paddle. In some instances, although the lead edge of the envelope does reach the vertical surface, the envelope becomes pinched too tightly between the rest of the stack and the guide and therefore the bottom edge does not come to rest on the horizontal surface. Thus, this envelope sticks up from the stack. At a minimum, this results in an uneven stacking of the envelopes that requires special attention of an operator. Even worse than the uneven stacking is that a jam may occur in the stacking bin.
Feed speed, ambient humidity levels, envelope size, envelope weight, envelope surface coefficient of friction and paddle spring force are some of the factors which influence whether or not the envelopes will stack tightly and properly registered along the vertical and horizontal surfaces. It is thus apparent that to compensate for these factors by manually adjusting the stacker system would require extensive trial and error. Thus, there is a need for an improved stacker system that automatically compensates for differences in these factors and produces a properly aligned and tight stack of envelopes under a wide range of operating conditions.
It is an object of the present invention to provide an improvement to the stacker system that substantially alleviates the aforementioned problem.